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Can we have some more data, please?The FDA threw Sarepta Therapeutics(NASDAQ:SRPT) a curve in November, when it told the biotech that it shouldn't even bother applying for accelerated approval for its Duchenne muscular dystrophy drug, eteplirsen. The last communication from the FDA was more along the lines of "send us the phase 2 data you have now, and we'll take a look."

It appears the failure of Sarepta's competitor, drisapersen, a drug from Prosensa(NASDAQ:RNA) and GlaxoSmithKline(NYSE:GSK), had a lot to do with the change of heart. The lack of a long-term control group -- patients that initially got placebo were switched to eteplirsen -- also affected the decision.

Sarepta and the FDA are still in discussions as to exactly what a phase 3 trial will look like. Whatever the design, we're looking at a delay of more than a year, possibly more.

Let's figure out how safe your approved drug really isThe FDA approved Ariad Pharmaceuticals' (NASDAQ:ARIA) blood cancer drug Iclusig at the end of 2012 despite a few patients in the clinical trials experiencing blood clots. As the biotech continued to follow patients post-approval, the blood clots didn't go away. In fact, the longer patients were on the drug, the more likely they were to develop a blood clot. Time apparently doesn't heal all wounds.

The FDA eventually decided that the risk wasn't worth the reward for all the patients Iclusig was approved for and asked Ariad to pull the drug from the market. Ariad and the FDA are in talks to define the patient population that can use Iclusig and hopefully get the drug back on the market. Certainly those that have had previous heart attacks or strokes will be excluded, but the drug's use might be further limited to just patients that don't have any other option. A chance of getting a blood clot trumps a guarantee of dying from leukemia.

I know what we said, but ...When designing its clinical trials, Amarin(NASDAQ:AMRN) did everything right. The biotech went to the FDA, asked exactly what the agency wanted to see before approving its lipid-lowering drug Vascepa, and got it in writing in the form of a special protocol assessment, or SPA.

The SPA said that if Amarin could show that Vascepa lowered triglycerides in patients with moderately high triglyceride levels, the biotech could apply for approval for that population once an outcomes trial was substantially enrolled.

But the FDA reneged on the SPA this year, citing clinical trials that concluded after the SPA was put in place, which showed drugs could lower triglycerides but not improve clinical outcomes. It appears the agency wants to see the results of Amarin's outcomes study before approving the drug.

Learning for 2014The lesson here is clear: Nothing is set in stone. The FDA can and will change its mind if new data comes to light. While binary events likes FDA decisions and clinical trial results remain the most risky part of investing in the sector, investors should factor into their risk-reward scenarios the possibility for delays in approvals and even the potential for drugs already on the market to be removed.